AB0852 CLINICAL CHARACTERISTICS, MYOSITIS AUTOANTIBODY PROFILE AND EARLY TREATMENT RESPONSE IN IDIOPATHIC INFLAMMATORY MYOSITIS - A SINGLE CENTRE EXPERIENCE FROM SOUTH INDIA
Authors: H. Gangadharan, R. Thomas, R. T R
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Idiopathic inflammatory myopathies (IIM) is a rare heterogenous group of diseases with varying involvement of muscle, skin, joints and lung. There is a paucity of prospective cohort studies in IIMs from India which assess the treatment response and clinico serological profile of patients with IIM. <h3>Objectives</h3> To describe the clinical characteristics, autoantibody profile and early treatment response in a prospective cohort of patients with IIM attending the Rheumatology clinic of a tertiary care teaching hospital in South India between October 2020 and June 2022. To compare IIM patients with interstitial lung disease (ILD) and IIM patients without ILD. <h3>Methods</h3> A prospective cohort of 37 consecutive adult patients fulfilling the 2017 EULAR ACR classification criteria of IIM was studied. The demographic data and clinical characteristics was recorded using a structured proforma. Muscle power was assessed by manual muscle testing (MMT8) in all patients. Myositis specific autoantibodies (MSA)and myositis associated autoantibodies (MAA) to 16 antigens were performed in all patients by line blot assay using Euroimmun (Luebec, Germany) as per manufacturer's instruction. All patients with MMRC grade 2 or more dyspnoea and/or dry cough and a restrictive pulmonary function test underwent HRCT chest for the diagnosis of ILD. Treatment response was assessed at 6 months based on the 2016 ACR/EULAR criteria for minimal, moderate and major clinical response. The various demographic, clinical and serological parameters were compared between patients with ILD and those without ILD. Comparisons between groups were made with the chi-squared test/Fisher's exact test when testing categorical variables and the Mann-Whitney <i>U</i> test or Independent samples' t test for continuous data. Multivariate analysis was done to find the independent factors associated with interstitial lung disease. <h3>Results</h3> 24 patients were female (64.9%) and the mean age of the study population was 46.7 ± 14 years. The median disease duration was 8 months (13 months). The most common symptoms were dyspnoea (59.5% of patients), proximal muscle weakness (56.8%), SICCA (35.1%) and photosensitive rash (32.4%). Mechanics hand was seen in 29.7% of patients, heliotrope rash in 24.3%, Gottron's papule in 18.9% and Gottron's sign was seen in 16.2% of patients. The median creatinine kinase (CK) level was 309 Units/L (1794) and median MMT 8 score was 78. 15/37 patients (40.5%) had dermatomyositis, 13/37 (35.1%) patients had anti synthetase syndrome, 4/37(10.8%) had biopsy proven necrotizing myopathy, 3/37 (8.1%) had overlap myositis and 2/37 (5.4%) had pure polymyositis. The most common MSA was anti Jo1 (7/37, 18.9%) followed by anti MDA5 (5/37, 13.5%) and anti PL12 (4/37, 10.8%) and the most common MAA was Ro52 (6/37,16.2%). 7/37 patients (18.9%) were negative for any of the MSA/MAA. Clinically amyopathic myositis was seen in 19/37 (51.4% of patients). ILD was seen in 20/37 patients (54.1%) and rapidly progressive ILD (RP ILD) was seen in 5/20 ILD patients (25%). The most common immunosuppressive agent used was corticosteroid (37/37) followed by mycophenolate mofetil (17/37,45.9%), methotrexate (9/37, 24.3%) and Rituximab (7/37,18.9%). After 6 months of treatment, 13/37 (35.1%) patients showed major response, 16/37 (43.2%) moderate response and 3/37(8.1%) patients showed minimal response. There were 5 deaths, 3 of which was due to pneumonia, 1 due to RP ILD, and 1 due to respiratory muscle weakness. On univariate analysis median disease duration, arthritis, CK levels, MDA 5 positivity and MSA/MAA positive status were associated with ILD. However, on multivariate analysis none of the factors showed any significant association with ILD. <h3>Conclusion</h3> The frequency of ILD is high in our cohort of IIM patients and as a significant proportion had no objective muscle weakness, the use of myositis autoantibody panel is warranted for early detection of such cases. <h3>Acknowledgements</h3> Department of Pulmonary Medicine, Government Medical College Kottayam, Kerala, India. <h3>Disclosure of Interests</h3> None Declared.